1. Field of the Invention
This invention relates to an image read-out apparatus for reading out an image such as a radiation image. This invention particularly relates to an improvement in a light detection means of the image read-out apparatus.
2. Description of the Prior Art
There have heretofore been widely used image read-out apparatuses wherein an image recorded on a sheet is read out by two-dimensionally scanning the sheet with a light beam such as a laser beam, and detecting light carrying the image information obtained by exposure of the sheet to the light beam, such as light reflected by the sheet, light transmitting through the sheet, or light emitted by the sheet, by use of a light detection means provided with a photomultiplier or the like.
The image read-out apparatus of this type is used, for example, as a scanner for plate making, an input apparatus for a computer or a facsimile, and a radiation image read-out apparatus in a radiation image recording and reproducing system using a stimulable phosphor sheet as disclosed, for example, in U.S. Pat. Nos. 4,258,264 and 4,346,295, and Japanese Unexamined Patent Publication No. 56(1981)-11395.
Specifically, when certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor. In the aforesaid radiation image read-out apparatus, a radiation image of an object such as the human body is stored on a sheet provided with the stimulable phosphor, the stimulable phosphor sheet carrying the radiation image is then scanned with stimulating rays such as a laser beam which cause the sheet to emit light in proportion to the stored energy of the radiation, and the emitted light is photoelectrically detected to obtain an image signal.
FIG. 25 shows an example of the aforesaid radiation image read-out apparatus, the mechanism of which will be described below.
Stimulating rays 101a of a predetermined intensity are emitted by a stimulating ray source 101 to a galvanometer mirror 102. The stimulating rays 101a are deflected by the galvanometer mirror 102 and made to impinge upon a stimulable phosphor sheet 103 positioned below the galvanometer mirror 102 so that the sheet 103 is scanned by the stimulating rays 101a in the main scanning direction, i.e. in the width direction of the sheet 103 as indicated by the arrow A. While the stimulating rays 101a are impinging upon the stimulable phosphor sheet 103, the sheet 103 is conveyed in the sub-scanning direction as indicated by the arrow B, for example, by an endless belt device 109. Therefore, scanning in the main scanning direction is repeated at an angle approximately normal to the sub-scanning direction, and the whole surface of the stimulable phosphor sheet 103 is two-dimensionally scanned by the stimulating rays 101a. As the stimulable phosphor sheet 103 is scanned by the stimulating rays 101a, the portion of the sheet 103 exposed to the stimulating rays 101a emits light having an intensity proportional to the stored radiation energy. The light emitted by the stimulable phosphor sheet 103 enters a transparent light guide member 104 from its light input face 104a positioned close to the sheet 103 in parallel to the main scanning line. The light guide member 104 has a flat-shaped front end portion 104b positioned close to the stimulable phosphor sheet 103 and is shaped gradually into a cylindrical shape towards the rear to form an approximately cylindrical rear end portion 104c which is closely contacted with a photomultiplier 105. The light emitted by the stimulable phosphor sheet 103 upon stimulation thereof and entering the light guide member 104 from its light input face 104a is guided inside of the light guide member 104 and up to the rear end portion 104c, and received by the photomultiplier 105 via a filter (not shown) for selectively transmitting the light emitted by the stimulable phosphor sheet 103. Thus the light emitted by the stimulable phosphor sheet 103 in proportion to the radiation energy stored thereon is detected and converted into an electric image signal by the photomultiplier 105. The electric image signal thus obtained is sent to an image processing circuit 106 and processed therein. The electric image signal thus processed is then reproduced into a visible image and displayed, for example, on a cathode ray tube (CRT) 107, or stored on a magnetic tape 108, or directly reproduced as a hard copy on a photographic film or the like.
In the aforesaid radiation image read-out apparatus, the light detection means used for detecting the light emitted by the stimulable phosphor sheet 103 comprises the photomultiplier 105 and the light guide ember 104. However, the light guide member 104 used in the conventional apparatus is fabricated to guide the light entering from the light input face 104a positioned along the main scanning line through total reflection to the photomultiplier 105 which has a small width in the main scanning direction. Therefore, the light guide member 104 becomes large, and consequently the whole read-out apparatus provided with the light guide member 104 becomes large. Further, the light guide member 104 has the drawback that a part of the light guided through total reflection inside of the large light guide member 104 is not totally reflected because of angle-related factors and passes through the light guide member 104, and therefore the light guide efficiency becomes low. Also, the light guide member 104 is fabricated of a light guide sheet member such as an acrylic plate by forming one end which corresponds to the light input face into a linear shape and the other end which corresponds to the light output face into a shape (for example, a cylindrical shape) which matches the light receiving face of the photomultiplier 105. Therefore, the fabricating process becomes complicated, and the manufacturing cost becomes high. As a result, the manufacturing cost of the radiation image read-out apparatus becomes high.